Which one of the following best characterizes the solution in the flask past the

Question

Which one of the following best characterizes the solution in the flask past the equivalence point of the titration? Circle the correct answer. a) a solution of a strong acid b) a solution of a weak acid c) a buffer solution d) solution of a strong base e) a solution of a weak base f) a neutral solution The curve below corresponds to the titration of 80.0 ml of acid with 0.40MNaOH. What is the concentration and pK_a of the acid in the flask? Circle the correct answer and show work in the box. (a) 0.24 M acid with pK_a = 9.0 (b) 0.24 M acid with pK_a = 3.0 (c) 0.060 M acid with pK_a = 3.0 d) 0 0.060 M acid with pK_a = 5.0 (e) 0.24 M acid with pK_a = 5.0 (f) 0.060 M acid with pK_a = 90 A volume of 10.0 mL of H_3PO_4 was titrated with 0.10 M NaOH. The pH response to addition of various amounts of NaOH is shown below. a) Circle the correct answer. At point C the ratio of [H_2PO_4^-]/[HPO^2-_4] is: A. 2; B) 1 C) 3; D) 4 What is the volume of NaOH added to reach the

Explanation / Answer

C)

Q10

V = 80 ml of acid ´+ 0.40 M o fNaOH

find pKa from the solution...

From the graph, we know that:

there is buffer formation in the interval between V = 0 and V = 12.5 mL

so...

the best way to predict pKa, is via

pH = pKa + log(A-(/HA)

we can choose any point, but it is easier to get the HALF equivalence point

equivalence point = V = 12 mL, then V = 12/2 = 6 mL is the half point

pH at V = 6 mL -- >5

therefore

pH = pKa + log(A-/HA)

5= pKA + log(1)

pKa = 5

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